Throughout this application various publications are referred to by number in square brackets. Full citations for the references may be found at the end of the specification. The disclosures of each of these publications, and also the disclosures of all patents, patent application publications and books recited herein, are hereby incorporated by reference in their entirety into the subject application to more fully describe the art to which the subject invention pertains.
MRI RF coil performance evaluation is an important aspect of clinical MRI quality assurance. RF coil performance is usually evaluated with region-of-interest (ROI) analysis from a single or multiple 2D phantom composite images [1, 2]. This simple approach has worked quite well for large volume coils (e.g., quadrature body or head coil) or phased-array coil with large receivers [3]. With the rapid development of coil technology and the wide application of parallel imaging, the number of coil receivers is increasing rapidly and the size of each receiver becomes small [4-6]. This has led to high density phased-array coils, characterized by 3D array arrangement of their multiple receivers. Coils with more than 96 and 128 channels have been proposed for clinical and research MRI [5, 7, 8]. These coils are highly costly but have much higher signal-to-noise ratio (SNR) compared to similar volume coils, especially in areas close to the coil. If one channel fails to work, the small region near the bad channel may have much reduced SNR but the overall composite images may look just normal. This reduced SNR may have an important impact in clinical and research MRI studies. For instance, functional activation in a cortical region in a BOLD (blood oxygenation level dependent) study may not be detected if the coil SNR at that region is compromised. In addition, excessive parallel imaging aliasing artifacts simulating pathological conditions may be generated when one or some of the channels fail to work [4, 6, 9]. It is therefore imperative to look into the function of each individual receiver to make sure the overall performance of the coil is at its optimum.
It is now required that a thorough annual performance survey has to be included for the ACR MRI Accreditation Program. This annual performance survey includes B0 homogeneity test and standard tests on the ACR phantom, and a complete check of all the clinical coils. However, the specific approach to checking the function of the coils is not outlined by the guideline, and is left to the MRI expert who is conducting the survey. Most physicists only look at a single composite image and/or obtain SNR from a single area of the coil. This may result in problems from defected channels being missed. In a recent presentation, it was found that 25% of all phased-array RF coils have at least one bad channel [10]. It is recommended that each channel of every phased-array RF be tested. This process, however, is very time consuming and may take 4-8 hours to complete depending on the number of coils and number of receivers of the coils.
The present invention address the need for improved performance assessment methods.